Respiration of `Hass' Avocados in Response to Elevated CO2 Levels

Abstract

Stress levels of carbon dioxide can be effective in the retardation of ripening and control of decay-causing pathogens and insect infestation of some horticultural perishables. Our objective has been to identify key mitochondrial enzymes and pathways that regulate the fruit's response to CO2 actions. Oxygen uptake of fruit stored in air + 20% CO2 (16.8% O2) was depressed compared to the airstored fruit, whereas the fruit stored in air + 40% CO2 (12.6% O2) had an elevated respiration rate. Climacteric fruit treated with 20% CO2 at 10C had increased pyruvate dehydrogenase (PDH) activity, decreased cytochrome oxidase (CytOx) activity, and double the alternative oxidase (AltOx) activity compared to air-stored fruit. Air + 40% CO2-stored fruit had reduced PDH and CytOx activities, and 50% more AltOx activity than the control fruit. Mitochondria were treated directly with the same CO2-enriched atmospheres to measure the catalytic effects of CO2. Total O2 uptake was decreased in both CO2 atmospheres and the cytochrome/alternative pathway ratio was greater than with mitochondria held in air. Nuclear magnetic resonance analysis of whole fruit confirmed that these CO2 atmospheres decrease the intracellular pH several 0.1 pH units with 2 h.